The Gulfstream IVSP Sees Inside Fabian

The NOAA Gulfstream IV-SP (G-IV) flew into the eye of Hurricane Fabian, a Category 4 storm, on September 1st, 2003. The aircraft launched from St. Croix at 1251 EDT and landed back in St. Croix at 1607 EDT. On September 1st, Fabian was located about 450 miles northeast of the U.S. Virgin Islands. From Air Force Reconnaissance aircraft reports, the storm slightly intensified from 946 mb at 1 pm EDT to 942 mb at about 3 pm on September 1st. The five-person crew, all from AOC, were testing the aircraft response to meteorological conditions near the core of a strong hurricane.

Flying at 41,000 feet, and approaching Fabian's eye from the southwest, the crew noted a well-formed eye on radar, stronger on the north side than on the south and west. Arriving at a point about 50 miles south of the eye, after thorough analysis of the storm using radar, they decided to head for the center. Once through the south eyewall, the pilots turned to the southwest over the Fabian's circulation center, and the crew released four dropwindsondes (more information about dropwindsondes can be found at the University Corporation for Atmospheric Research web site) while inside the eye. These dropsondes used GPS navigation and meteorological sensors to measure temperature, humidity, pressure, wind direction and wind speed as they descended in Fabian's eye. One dropwindsonde measured a low-altitude wind gust of 71.2 m/s, or about 138 knots, and all of the sondes inside the eye measured surface pressures below 950 millibars. The G-IV exited the eye to the southwest.

The crew's experience up to this point was smooth to light chop everywhere exept the eyewalls, moderate turbulence in the eyewall, so they decided to fly the second objective, surveying the area between eyewall and first rainband. The aircraft tracked first northwest, then southwest keeping the eyewall reflectivity maximum on the 25-mile radar ring. While flying the survey pattern outside of the eye, the eyewall became complete on the south side to form a perfectly closed eye with a 20 mile diameter. This radar information was relayed to the Air Force Reconnaissance plane, Teal 25, who was headed toward the center from the northeast. Completing the eyewall survey pattern west of the center, the G-IV crew headed back to St. Croix.

David Brogan with DropSonde